352 



7. INHIBITION IN MULTIENZYME SYSTEMS 



inhibitions of the steady-state rate of the cycle are also given in terms of 

 the inhibitions on the individual enzymes. Finally, in Fig. 7-29 are given 

 the inhibitions of the cycle rate in terms of inhibitor concentration and 

 they are compared with the inhibition of the single enzyme. For each inhi- 

 bition there are characteristic changes in the relative concentrations of 

 the cycle intermediates. The dependency of the cycle inhibition on the 



0.04- 



0.03 



0.02 



0.01 



— 0.08 



006 



0.04 



002 



(A) 

 (B) 

 (C) 



Fig. 7-18. Noncompetitive inhibition of Ej in the cychc system shown in Fig. 7-16. 

 (X) = 1 mil/ and (M), = 0.1 mM. 



enzyme inhibition varies with the particular enzyme inhibited and the 

 total concentration of cycle intermediates. 



Inspection of the curves will reveal in each case the behavior of the 

 system but a few general remarks may be made concerning the response 

 of such a cycle to inhibition. 



(1) A cyclic system generally possesses buffer capacity, in that the inhi- 

 bition of the cycle rate will usually be less than that of the enzyme that 

 is affected. However, in contrast to a linear chain, there will be no range 

 of absolute buffer capacity; any inhibition of a component enzyme will 

 depress the cycle rate to some extent. 



